This proposal requests support for the study of the genetic and biochemical nature of propionic acidemia, a disorder of organic acid metabolism caused by a deficiency of the biotin-dependent enzyme, propionyl CoA carboxylase. The major objectives are to characterize biochemically and immunologically normal and mutant propionyl CoA carboxylase as a model for elucidating the expression and gene regulation in the homozygous and heterozygous state and to investigate the metabolism of biotin in the normal and homozygous state. We will prepare antibodies to human propionyl CoA carboxylase from liver by exploiting the unique interaction of avidin to biotin and biotin-containing enzymes. These antibodies will be used to characterize the molecular structure of normal and mutant enzymes, to elucidate the biochemical mechanism of genetic complementation, and to determine the unusual differences between heterozygotes. In addition, we will use these antibodies and biotin-deficient fibroblast cultures to investigate the metabolism of biotin in man and its role in the treatment of propionic acidemia.